1. Field of the Inventions
The present invention relates to a steering system for a small boat with a propulsion unit such as outboard motor or stem drive.
2. Description of the Related Art
A steering system for a boat propulsion unit such as outboard motor, is disclosed in Japanese Patent Document JP-B-Hei 6-33077. This steering system is designed to control the delivery amount of hydraulic fluid so as to achieve fast steering movements during low speed (boat speed) operation and slower steering movements during higher speed (boat speed) operation. Boat speed can be detected by a speed sensor provided on the outer bottom surface of the boat.
Variable steering ratio steering systems for automobiles, on the other hand, are disclosed in Japanese Patent Document JP-B-3232032. This steering system is designed such that a target steering angle ratio (ratio of steering wheel movement to change in steering angle of front wheel of vehicle) is adjusted in response to changes in a vehicle speed signal from a vehicle speed sensor. The steering angle ratio is controlled based on the target steering angle ratio and an actual steering angle ratio.
Small boats with outboard motors tend to have certain common steering properties. For example, these boats can be steered by turning the steering wheel which causes the outboard, motor to pivot in a lateral direction, about a vertical shaft, thereby propelling the boat in a direction toward which the outboard motor has been moved. At low boat speeds, thrust is relatively small, and the ratio of a propulsion unit angle (steering angle) to the amount of steering wheel displacement can be increased to deflect the outboard motor by a larger amount relative to the amount of movement of the steering wheel to provide more responsive boat behavior.
These boats are also often countersteered against the wind and tides so as to maintain a straight heading. For example, the steering wheel can be turned by a small amount and held at that position so that the propulsion unit counteracts the forces of the wind or tides, and thus maintain a desired heading.